The invention relates to a method for controlling the generation of suds in a washing machine, especially during the treatment of washing with suds in a program-controlled washing machine, as well as to a washing machine especially suitable for carrying out this method.
With known washing methods the laundry to be washed is simply mixed with a quantity of water or washing liquid, also known as “liquor”, which is sufficient for the laundry to be washed to be saturated with water and for a minimum of free washing liquor, generally 2 to 3 liters, to make possible an exchange of material between the heater for warming the washing liquor and the laundry. The free liquor corresponds to that residue of the washing liquor that is not bound by the laundry and is thus present as liquid. The corresponding dimensioning of the quantity of water of washing liquor is ensured by a suitable method for regulating the water level in the drum and adapting the quantity of water to the absorption capability of the laundry. The free liquor is produced after subtracting the quantity of water bound into the laundry from the quantity of water with which the washing machine is filled. Woolen fabric binds around 200% of its own weight, so that a load of 6 kg or woolen fabric binds in around 12 liters of water.
The energy consumption of a washing machine is essentially determined by the energy needed for heating up the water. A reduction in the amount of water would thus be desirable, especially a reduction in the amount of free liquor. However the free liquor must guarantee the transport of heat from the heater into the laundry. A reduction in the liquor and thereby a reduction in the energy consumption are thus difficult to achieve.
An alternative to this known washing method is washing with suds which can be generated by adding mechanical energy into the washing liquor. In such cases the suds take over the heating up and cleaning of washing to be cleaned.
To achieve a sufficient energy transport from the heating device in a washing machine into the washing it is necessary to develop sufficient suds. Because of the lower heat capacity of suds compared to the heat capacity of a washing liquor there would otherwise be the danger of the heating device overheating. However, if too many suds are generated, there is the danger of the suds escaping from the washing machine, especially from its dispensing compartment. In addition it should be noted that the development of suds depends on a large number of parameters. Some of the parameters can be influenced by a program-controlled washing machine by a corresponding design of the appropriate washing programs (for example temperature, amount of water, speed of the drum). Type and quantity of laundry as well as the detergents (tensides and further substances) as well as water hardness and degree of contamination on the other hand are not able to be influenced by a washing machine and are subject to unpredictable fluctuations from application to application.
DE 43 34 969 A1 describes a device for generating washing suds in a washing machine with a rotatable drum in a tub, having a facility for generating hot air which is introduced by a inlet feed in the tub wall between the tub and the drum.
In accordance with publication DE 41 04 151 A1, undesired suds occurring in a washing machine are destroyed by switching on a heating device. In order to also destroy the suds further away from the heating device, the drum is turned slowly, so that further suds reach the heating device and are destroyed there by being heated up.
In addition methods are known from DE 102 34 472 A1 and also DE 198 46 248 A1 for removing suds in a tub of a drum washing machine.
DE 102 34 472 A1 discloses a method for removing suds in a tub of an electronically controlled drum washing machine as a result of a program step provided for draining water from the tub, with a liquor draining system arranged on the floor of the tub with a liquor pump and with a sensor for determining the level of fluid to be found in the tub. The curve of the sensor signal (P) which is recorded during the operation of the liquor pump contains a gradient Δpn/Δtn by comparison with Δpn-1/Δtn-1, which indicates the presence of suds, whereupon a suds handling measure matched to the gradient is initiated.
In EP 0 278 239 A1 a disproportionate suds formation in the main washing process, which is to be observed during heating of washing liquor in the tub, is removed by adding a restricted amount of cold water by temporarily disconnecting the liquor heater.
EP 0 268 155 A2 describes a washing machine with a facility for preventing the formation of foam. To this end a washing machine with a so called foam preventer is proposed, with the speed of a washing drum drive motor being reduced until such time as the foam limit has returned to below a specific low level, which is then permanently maintained.